This invention relates to rotary valves and, in particular, to rotary valves for use in controlling an air supply to alternating pressure patient support systems.
Alternating pressure mattresses are commonly used for prevention and treatment of pressure sores and alternating pressure pads have been used in other patient support equipment, such as wheelchair cushions. Alternating pressure systems are linked to a pump or other source of air pressure via a control system which alternately inflates and deflates different cells or sets of cells within the patient support structure. The variation in interface pressure between the patient""s skin and the mattress reduces the incidence of pressure sores.
Two methods have been used to distribute air to and from the mattress cells in order to produce the alternating pressure effect. These are rotary valves and multiple solenoid valves. Rotary valves which have been used in the past have included an actuator plate continuously rotating against a valve face. The actuator plate is formed with slots and holes which periodically align with holes in the valve face, thus opening and closing air ports. The cycle time is governed by the speed at which the actuator rotates across the valve face and the timing of each opening and closing event is determined by the positions and dimensions of slots and holes in the valve assembly and the speed of rotation.
Although rotary valves of this type are relatively inexpensive, simple and reliable, they have the disadvantage that continuous operation of the motor increases power consumption and the timing of the opening and closing events within one cycle is fixed.
The second method of controlling alternating pressure mattresses and other support systems are solenoid valves. Although solenoid valves can be readily controlled by a micro- processor, they have the disadvantages that they are relatively expensive and give limited flow rate so that large capacity valves are required. They are also relatively noisy, tend to be unreliable in use and have a high power consumption.
The present invention provides an improved rotary valve system which combines most of the advantages of conventional rotary and solenoid valves.
According to one aspect of the present invention, there is provided a rotary valve for controlling air supply to an alternating pressure patient support system which comprises a body member having a planar surface and at least two apertures for communication with cells and/or sets of cells in the patient support system, and a further aperture for connection to a pressurized air source, and actuator member which is rotatable in face to face contact with said planar surface, said actuator having a recessed portion which forms an air supply chamber when in contact with said planar surface and is positioned to be constantly supplied with air from said further aperture, drive means for rotating the actuator with respect to the first member and detector means for detecting the position of the actuator relative to the body member, and in conjunction with control means, for controlling the timing and duration of air supply to the cells or sets of cells.
Preferably, the actuator also includes an aperture through which air can be exhausted in turn from one or other of the cells or sets of cells.
The detector preferably comprises at least one optical sensor mounted in the vicinity of the actuator and arranged to detect the position of the actuator relative to the body member. In one embodiment, the sensor interacts with apertures or slots in the actuator which are conveniently located around the perimeter.
Preferably, the drive means is capable of rotating the actuator in both directions and this gives greater flexibility to the sequence of events, timing and duration of air supply to the cells.
Finally, many other features, objects and advantages of the present invention will be apparent to those of ordinary skill in the relevant arts, especially in light of the foregoing discussions and the following drawings, exemplary detailed description and appended claims.